A disk drive is a data storage device that stores data in concentric tracks on a recording media disk. During operation, the disk is rotated about an axis by a spindle motor while a transducer (head) reads/writes data from/to a target track of the disk. A servo controller uses servo data read from the disk to accurately position the head above the target track while the data transfer takes place. Cross-track density is an important characterization of the storage capability for a given disk drive. Cross-track density (e.g., tracks/inch) is a function of head design as well as the physical qualities of the recording media. Adjacent track erasure, which may limit the cross-track density, occurs when data stored on a first track is corrupted by the writing of data to a second track, adjacent to the first track. Bit error rate (BER) and data loss specifications for a disk drive may therefore limit the cross-track density and overall storage capacity.
Typically, the cross-track density capability of a recording media is measured one of two ways. In the first method, a recorded signal's amplitude change induced by partially erasing a written track with a nearby track write is measured (e.g., a “squash,” or “squeeze,” measurement). In the second method, an error rate change induced by partially erasing a written track with a nearby track write is measured (e.g., an “off-track read capability (OTRC),” or “747” measurement). A squeeze measurement provides a rapid, but relatively inaccurate, spinstand-based characterization of a recording media. An OTRC measurement provides an accurate, but relatively slow, characterization of a recording media in an assembled disk drive. For example, a single OTRC measurement may take many hours or even days to complete because tens of thousands of read/writes are performed.